1. Field of the Invention
The present invention relates to a developing apparatus of an electrophotographic type image forming apparatus installed according to a monochrome/color and standalone/network connection type of copying machine, printer, facsimile, complex machine of them, and the like, and an image forming apparatus provided with the same.
2. Description of Related Art
Conventionally, in an electrophotographic developing apparatus, a mono-component development and a two-component development are employed. In the mono-component development, since a toner comes into contact with each of members of a developing device in a portion supplying the toner, a portion charging the toner, a portion discharging the toner, and a portion recovering the toner, a load is applied to the toner. A thermoplastic resin is used for the toner, and inorganic fine particles are attached and treated as a fluidity modifying agent to the surface thereof. Accordingly, the toner surface is thermally changed and the inorganic fine particles are embedded due to the load. Since a rotating speed of each of the members becomes high in a high speed machine, a greater load is applied to the toner. Therefore, a speeding up has a limit. Further, in recent years, a diameter of the toner is significantly reduced according to a high image quality and is frequently set to be equal to or less than 6 μm. Since a larger amount of after treatment agent is treated for the toner having the small diameter as mentioned above, and the fluidity is deteriorated, an aggregation of the toner and the embedding of the after treatment agent are significantly caused by the load mentioned above. Further, a tendency of a low temperature fixing is significant as an environmental countermeasure. Accordingly, a thermal resistance of the toner is lowered, causing a further disadvantageous condition with respect to the load mentioned above.
In the two-component development, a toner charged due to triboelectric charging between the toner and a carrier is attached to an electrostatic latent image formed on an image carrier so as to develop. Within a developing device, a charged state of the toner is maintained by keeping a rate of the toner and the carrier constant. However, if the electrostatic latent image formed on the image carrier is developed with the toner, the toner comes short. Accordingly, the toner is replenished by a replenishing section. The toner replenished by the replenishing section is not charged yet, and is charged while being agitated and conveyed with a developer within the developing device by an agitating and conveying section within the developing device. In this method, since the charging application is carried out by mixing the particles, the load applied to the toner is small. Accordingly, the toner has a longer service life in comparison with the mono-component development, and an excellent high speed response can be obtained.
On the other hand, in recent years, an electrophotographic type of product has been introduced in a field of a high production region, a system having a high speed and a long service life has been proposed. In the developing apparatus, there have been provided an apparatus having a plurality of developing rollers, an apparatus having a trickle mechanism gradually replacing a developer, a hybrid developing apparatus using a two-component developer for a supply roller portion and a mono-component toner for a developing roller portion, and a developing apparatus obtained by combing them. In any developing apparatus, the toner is replenished, and the toner is charged while being agitated and conveyed with the developer within the developing device by the agitating and conveying section within the developing device.
In the toner replenishing type developing apparatus, if a high printing rate of print is continuously carried out, the toner comes short and the uncharged toner is accordingly replenished. Then, if the replenished toner is conveyed in a state in which a charged amount is low, without being sufficiently agitated, and is supplied onto the developing roller, image deterioration such as toner scattering and toner fogging occurs.
Further, since a time for which the replenished toner is conveyed onto the developing roller becomes short due to the recent speeding up of the apparatus, the problem mentioned above becomes further serious. Then, there has been proposed a developing device using two agitating members for providing a developing device which efficiently and well agitates a developer as well as preventing the replenished toner from being conveyed onto the developing roller without being sufficiently agitated, and has no fogging and no scattering.